A core/shell nanoparticle consists of an iron oxide core fully covered by at least one metal shell. A capping layer may optionally be present on the core/shell nanoparticles. The ability to control the size and mono-dispersity in synthesizing and assembling metal-coated superparamagnetic nanoparticles is important in technological applications of the nanoscale core, shell or their combinations. Size control and mono-dispersity is increasingly important for many applications involving magnetic nanoparticles such as magnetic resonance imaging for medical diagnosis, high-density magnetic recording, controlled drug delivery, biological targeting or separation, ferrofluids and catalysis.